Thermistor system for temperature measurement in a gas water heater combustion chamber

ABSTRACT

A gas water heater that includes a sheathed thermistor placed into the combustion chamber near a gas burner to provide for more accurate measurements of the temperature therein. The thermistor may be used in combination with a thermopile to provide additional measurements for determination of temperature conditions requiring a closure of a valve controlling the flow of gas to the burner

FIELD OF THE INVENTION

The subject matter of the present disclosure relates generally to temperature measurement in the combustion chamber of a gas water heater.

BACKGROUND OF THE INVENTION

A variety of energy sources are used in creating hot water for commercial and residential use including electric, solar, and various fuels. Natural gas and propane are preferred by some customers due to e.g., the relatively quick heating rate. These fuels are supplied as a gas that is burned in a combustion chamber to provide heat energy to raise the water temperature.

Temperatures in the combustion chamber are relatively high and can e.g., reach 600 degrees Fahrenheit during normal operation. A flame is created by burning a mixture of the gaseous fuel and air. Proper combustion requires that the air and fuel are provided within a particular ratio to ensure e.g., complete combustion and avoid wasted fuel or the production of unwanted by-products such as carbon monoxide.

If the water heater is e.g., installed in a dusty area containing above average levels of e.g., dirt, oil, or lint, the air intake of water heater can become clogged. The lack of enough air can cause the temperature of the combustion chamber to become too hot. As another example, a flammable vapor event such as a the ignition of vapor from liquid fuel present near the water heater can also create elevated temperatures in the water heater combustion chamber.

Accordingly, it is desirable to monitor temperature and terminate the combustion process by e.g., shutting off the gas flow if the temperature reaches unsafe levels.

One conventional approach is the use of a bi-metal switch placed in direct contact with the wall of the combustion chamber so as to activate the switch. The metals of the bi-metal switch have different thermal expansion characteristics. Once the temperature of the bi-metal switch reaches a predetermined maximum temperature, the switch is activated so as to cause a control system to close off the flow of gas—even if the temperature is only high for a relatively short period of time. Then, the bi-metal switch must cool before allowing the water heater to operate again or, alternatively, the bi-metal switch must be manually reset. Such reset requirement can be undesirable, particularly if the increased temperature was not due to a unwanted event such as clogging of the air flow.

Also, because the bi-metal switch must be placed in contact with the combustion chamber wall, it does not provide a direct measurement of the temperature of the combustion process. Instead, heat must be transmitted to the wall of the combustion chamber before the bi-metal switch can be triggered due to an unsafe condition. Furthermore, the bi-metal switch does not provide for multiple temperature measurements or adjustment of the temperature at which it is activated. Instead, the bi-metal switch is simply activated upon reaching a predetermined maximum temperature.

Accordingly, an improved system for measuring and monitoring the temperature of the combustion chamber of a gas water heater is needed.

BRIEF DESCRIPTION OF THE INVENTION

The present invention provides a gas water heater that includes a sheathed thermistor placed into the combustion chamber near a gas burner to provide for more accurate measurements of the temperature therein. The thermistor may be used in combination with a thermopile to provide additional, confirmatory measurements for determination of temperature conditions requiring a closure of a valve controlling the flow of gas to the burner. Additional aspects and advantages of the invention will be set forth in part in the following description, or may be apparent from the description, or may be learned through practice of the invention.

In one exemplary embodiment, the present invention provides a gas fueled water heater having a tank for storage of water for heating. A chamber wall at least partially encloses a combustion chamber. A gas burner is positioned adjacent to the tank and within the combustion chamber. The gas burner is configured for heating the water in the tank. A thermistor is positioned within the combustion chamber near the gas burner. The thermistor does not contact the chamber wall. The thermistor is configured for providing temperature measurements of the combustion chamber. A sheath is positioned around the thermistor.

In another exemplary embodiment of the present invention, a gas fueled water heater is provided that includes a tank for storage of water for heating. A chamber wall supports the tank and forms a combustion chamber. A gas burner is centrally located within the combustion chamber and is positioned below the tank. The gas burner is spaced apart from the chamber wall. A thermistor is located within the combustion chamber and is adjacent to the gas burner without being located within a flame of the burner. The thermistor is configured for providing a signal representing temperature within the combustion chamber. The thermistor is not in contact with the chamber wall. A sheath completely surrounds the thermistor and is configured for protecting the thermistor.

These and other features, aspects and advantages of the present invention will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

A full and enabling disclosure of the present invention, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended figures, in which:

FIG. 1 provides a partially cut away, side view of an exemplary embodiment of a water heater of the present invention.

FIG. 2 provides a perspective view of an exemplary gas combustion chamber as may be used with the exemplary water heater of FIG. 1.

FIG. 3 is a schematic of a gas flow control system as may be used with the exemplary water heater of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

Reference now will be made in detail to embodiments of the invention, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment can be used with another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents.

FIG. 1 illustrates a partial sectional, side view of an exemplary water heater 100 of the present invention. Water heater 100 includes a tank 102 where water is stored and heated. Water is supplied to tank 102 by inlet line 104. Heated water is supplied by tank 102 through outlet line 106. Water heater 100 is fluidly connected with lines 104 and 106 using connections 132 and 134. In turn, lines 104 and 106 connect with the water supply system of e.g., a residence or a commercial structure.

From line 104, water travels into tank 102 through a cold water dip tube 122 that extends along vertical direction V towards the bottom 114 of tank 102. After being heated, water exits tank 102 by travelling vertically upward and out through outlet line 106. Anode rod 126 provides protection against corrosion attacks on tank 102 and other metal components of water heater 100. A pressure relief valve 128 provides for a release of water from tank 102 in the event the pressure rises above a predetermined amount.

Water heater 100 includes a combustion chamber 110 in which a gas burner 108 is centrally located. Gas burner 108 is supplied with a gaseous fuel e.g., propane or natural gas. Air travels into combustion chamber 110 through air intake 112 in cabinet 130. The resulting mixture of air and gas is ignited and burned to heat bottom 114 of tank 102 and its water contents. Hot combustion gas 120 exits combustion chamber 110 through a vent or flue 124 centrally located within tank 102. Heat exchange with flue 124 also helps heat water in tank 102. A baffle 120 promotes this heat exchange. Gas 120 exits water heater 100 though vent hood 136, which may be connected with additional vent piping (not shown).

A thermostat 116 measures the temperature of water in tank 102 and provides a signal to gas control valve module 118. As used herein, “a signal” is not limited to a single measurement of temperature and, instead, may include multiple measurements over time or continuous measurements over time. Depending upon whether the desired temperature has been reached as determined e.g., from the signal from thermostat 116, gas control valve module 118 regulates the flow of gas to burner 108 as will be more fully described herein.

Referring now to FIG. 2, combustion chamber 110 is formed by a chamber wall 138 that at least partially encloses combustion chamber 110 and may also provide support for tank 102 along top edge 160. As shown, chamber wall 138 encircles burner 108 and is spaced apart from burner 108. Chamber wall 138 may be part of cabinet 130 (FIG. 1) or may be a separate component.

A thermistor 140 is positioned within combustion chamber 110 near gas burner 108 and is configured for providing a signal T_(S) representing the temperature in combustion chamber 110. As will be understood by one of skill in the art, a thermistor can include one or more resistors having a resistance in an amount that depends on the temperature. The amount of resistance can be correlated to temperature and used to provide a signal representing a measurement of the temperature. For water heater 100, the resistance to a current through the thermistor (and the changes in that resistance) provide a measurement of temperature in combustion chamber 110.

For this exemplary embodiment, thermistor 140 is located close to burner 108 without being directly in the flame 162 (FIG. 1) created by burner 108. Thermistor 140 does not contact chamber wall 138 as such might give an inaccurate temperature measurement. Instead, for this embodiment, thermistor 140 is supported on chamber wall 138 by a sheath 142 that surrounds thermistor 140 and connects with chamber wall 138 to support thermistor 140. For this exemplary embodiment, sheath 142 completely encloses thermistor 140. Sheath 142 protects thermistor 140 from damage by the heat and flame from burner 108 while still allowing conduction for temperature measurement. By way of example, sheath 142 may be constructed from a metal such as aluminum, a ceramic, and combinations thereof. Electrical conductors 144 connect thermistor 140 with gas control module 118 to provide the signal representing temperature from thermistor 140.

FIG. 3 provides a schematic representation of combustion chamber 110 and gas valve control module 118, which includes at least one controller 154. By way of example, controller 154 may include memory and one or more processing devices such as microprocessors, CPUs or the like, such as general or special purpose microprocessors operable to execute programming instructions or micro-control code associated with operation of water heater 100 as further described herein. The memory can represent random access memory such as DRAM, or read only memory such as ROM or FLASH. The processor executes programming instructions stored in the memory. The memory can be a separate component from the processor or can be included onboard within the processor. Alternatively, controller 154 may be constructed without using a microprocessor, e.g., using a combination of discrete analog and/or digital logic circuitry (such as switches, amplifiers, integrators, comparators, flip-flops, AND gates, and the like) to perform control functionality instead of relying upon software.

Water heater 100 includes a gas valve 146 positioned along main gas supply line 168. Controller 154 is in communication with gas valve 146 to control the flow of gas therethrough by determining when valve 146 is energized. For this exemplary embodiment, gas valve 146 operates so that when energized, valve 146 is fully open to allow a flow of gaseous fuel to burner 108. When not fully energized, valve 146 is fully closed (i.e. a “fail-closed” type valve) so as to prevent the flow of gaseous fuel to burner 108.

Water heater 102 includes a pilot burner 148 that provides a pilot light 150 to ignite the mixture of air and fuel at burner 108 when gas valve 146 is open. Gaseous fuel for pilot burner 148 is supplied by pilot burner fuel line 152. Gas valve control module 118 controls the flow of gaseous fuel through pilot burner fuel line 152. A thermopile 156 is positioned adjacent to the pilot burner 148. Thermopile 156 can convert heat from pilot burner 148 into electrical energy.

Thermopile 156 may be constructed from e.g., a plurality of thermocouples connected in a series, for example. The output voltage from thermopile 156 is proportional to the temperature. As such, thermopile 156 provides a signal to controller 154 through conductors 164 indicating whether a pilot light 150 is present at pilot burner 148. In addition, thermopile 156 can provide enough energy to power gas control module 118.

In one exemplary aspect of operation, if the signal from thermopile 156 indicates the measured temperature T_(P) is at room temperature (e.g., 72° F.), then the pilot light 150 is not present. In such state, gas valve 146 would remain unenergized or closed so that no gaseous fuel flows to burner 108. If the signal from thermopile 156 indicates a pilot flame 150 is present (e.g., temperature is above 500° F.), then module 118 can place gas valve 146 in either an open or closed state depending upon whether water in tank 102 needs to be heated. Specifically, by comparing temperature measurement using thermostat 116 with the desired set point temperature, module 118 can determine whether to open or close gas valve 146.

Additionally, if pilot light 150 is not present, gas control valve module 118 would also prevent the flow of gas to pilot burner 148 unless the user has placed gas control module 118 in a start or ignition state. In the ignition state, gas valve 146 would remain closed but module 118 would allow gas to flow through pilot burner fuel line 152 while igniter 158 (FIG. 2) provides one or more sparks so as to ignite gaseous fuel flowing from pilot burner 148 to create pilot light 150. Once pilot light 150 is detected by thermopile 156, controller 154 would continue to allow gaseous fuel to flow through pilot burner fuel line 152 while pilot light 150 is detected.

The signal from thermopile 156 can also be used to measure the temperature in combustion chamber 110. While the temperature measured at thermopile 156 may not be identical to the temperature as measured by thermistor 140, the signal from thermopile 156 can still be used to determine whether the temperature is such that the desired level of combustion it taking place in chamber 110. In addition, as stated, the signal from thermopile 156 provides a voltage sufficient to power controller 154 and other components of gas control valve module 118 such that an external power source is not required.

As previously described, for various reasons, the combustion of gaseous fuel in combustion chamber 110 may be incomplete—potentially creating carbon monoxide and undesirable, elevated temperatures. For example, air intake 112 may be clogged or blocked such that the supply of air for combustion is insufficient. As will now be further described, exemplary water heater 100 can detect when elevated temperatures are occurring and take precautionary steps.

In one exemplary aspect, controller 154 receives a signal from thermistor 140 representing the temperature in combustion chamber 110. When such temperature reaches or exceeds a predetermined maximum temperature, TS_(MAX), controller 154 terminates the flow of gaseous fuel to burner 108 by closing gas valve 146. As gas valve 146 is a “fail-closed” valve, controller 154 ceases to energize gas valve 146 thereby allowing a spring or other biasing element to force gas valve 146 into a closed state. In one exemplary embodiment of the invention, TS_(MAX) is 750° F. Other settings for TS_(MAX) may also be used, however.

It is desirable to avoid nuisance trips or unnecessary closings of gas valve 146. For example, if the temperature, TS, sensed by thermistor 146 is at or above TS_(MAX) only momentarily and then falls below TS_(MAX), then it may not be necessary to close gas valve 146 because e.g., incomplete combustion may not actually be occurring in chamber 110 or may have already ended.

Accordingly, in another exemplary aspect of the invention, controller 154 receives a signal from thermistor 140 representing the temperature TS in combustion chamber 110. When such temperature reaches or exceeds a predetermined maximum temperature, TS_(MAX), for at least a predetermined amount of time, Δ_(ts), then controller 154 terminates the flow of gaseous fuel to burner 108 by closing gas valve 146. In one exemplary embodiment, Δ_(ts) is ______ seconds. Other values may be used as well.

In another exemplary aspect of the invention, thermopile 156 can be used to provide a secondary measurement of temperature in combustion chamber 110 that can be used to determine whether to close gas valve 146. During operation of water heater 100, controller 154 receives a signal from thermistor 140 representing the temperature TS in combustion chamber 110 as measured by thermistor 140 and receives a signal from thermopile 156 representing the temperature TP in combustion chamber 110 as measured by thermopile 156.

By way of example, when the temperature TS as measured by thermistor 140 reaches or exceeds a predetermined maximum temperature, TS_(MAX), gas valve 146 it not closed unless the temperature TP as measured by thermopile 156 also exceeds a predetermined maximum value, TP_(MAX). In certain embodiments, TP_(MAX) is not necessarily the same value as TS_(MAX) and may be different due e.g., the difference in the location of thermistor 140 relative to thermopile 156. In one exemplary embodiment, TP_(MAX) is less than TS_(MAX). In still another exemplary embodiment, TS_(MAX) is less than 725° F. As such, if both TP and TS exceed TP_(MAX) and TS_(MAX), respectively, then controller 154 can operate to close gas valve 146. In this way, water heater 100 is able to avoid potentially unnecessary closings of valve 146 based on e.g., momentary temperature spokes detected thermistor 140.

In still another exemplary aspect, controller 154 receives a signal from thermistor 140 representing the temperature TS in combustion chamber 110. When such temperature ST reaches or exceeds a predetermined maximum temperature, TS_(MAX), for at least a predetermined amount of time, Δ_(ts), controller 154 does not close gas valve 146 unless the temperature TP as measured by thermopile 156 also exceeds a predetermined maximum value, TP_(MAX) for at least a predetermined amount of time, Δ_(tp).

In certain embodiments, Δ_(tp) is not necessarily the same value as Δ_(ts). In one exemplary embodiment, Δ_(tp) is less than Δ_(ts). In still another exemplary embodiment, Δ_(tp) is one second less than the value of Δ_(ts). Other values may be used as well. As such, if both TP and TS exceed TP_(MAX) and TS_(MAX) for predetermined time periods Δ_(tp) and Δ_(ts), respectively, then controller 154 can operate to close gas valve 146. Again, this exemplary aspect, water heater 100 is able to avoid potentially unnecessary closings of valve 146 based on e.g., momentary temperature spokes detected thermistor 140.

Accordingly, by using thermistor 140 placed in combustion chamber 110, more accurate temperature measurements of the combustion process can be provided to gas control valve module 118 with controller 154 than a typical bi-metal switch positioned against combustion chamber wall 138 as used in conventional constructions. In addition, thermistor 140 does not require a reset or period of cooling off as with such bi-metal switch constructions. In addition, one or more aspects as described above may be used with thermistor 140 to avoid unnecessary closings of gas valve 146.

This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims. 

1. A gas fueled water heater, comprising: a tank for storage of water for heating; a chamber wall at least partially enclosing a combustion chamber; a gas burner positioned adjacent to the tank and within the combustion chamber, the gas burner configured for heating the water in the tank; a thermistor positioned within the combustion chamber near the gas burner, the thermistor not contacting the chamber wall, the thermistor configured for providing temperature measurements of the combustion chamber; and a sheath positioned around the thermistor.
 2. The gas fueled water heater of claim 1, further comprising a controller in communication with the thermistor for the receipt of temperature measurements from the thermistor.
 3. The gas fueled water heater of claim 2, further comprising: a gas valve for controlling the flow of gas to the gas burner; wherein the controller is in communication with the gas valve and is configured to close the flow of gas through the gas valve upon determining that the temperature in the combustion chamber as measured by the thermistor has reached or exceeded a predetermined maximum temperature, TS_(MAX).
 4. The gas fueled water heater of claim 2, a gas valve for controlling the flow of gas to the gas burner; wherein the controller is in communication with the gas valve and is configured to close the flow of gas through the gas valve upon determining that the temperature in the combustion chamber as measured by the thermistor has reached or exceeded a predetermined maximum temperature, TS_(MAX), for a predetermined period of time, Δ_(ts).
 5. The gas fueled water heater of claim 1, further comprising: a pilot burner for providing a pilot light to ignite the gas burner; and a thermopile positioned adjacent to the pilot burner and configured for detecting the presence of a pilot light at the pilot burner.
 6. The gas fueled water heater of claim 1, further comprising: a pilot burner for providing a pilot light to ignite the gas burner; and a thermopile positioned adjacent to the pilot burner and configured for detecting the presence of a pilot light at the pilot burner and for providing a secondary measurement of temperature in the combustion chamber.
 7. The gas fueled water heater of claim 6, further comprising: a gas valve for controlling the flow of gas to the gas burner; wherein the controller is in communication with the gas valve and is configured to close the flow of gas through the gas valve upon determining that both i) the temperature in the combustion chamber as measured by the thermistor has reached or exceeded a predetermined maximum temperature, TS_(MAX), and ii) the temperature in the combustion chamber as measured by the thermopile has reached or exceeded a predetermined maximum temperature, TP_(MAX).
 8. The gas fueled water heater of claim 6, further comprising: a gas valve for controlling the flow of gas to the gas burner; wherein the controller is in communication with the gas valve and is configured to close the flow of gas through the gas valve upon determining that both i) the temperature in the combustion chamber as measured by the thermistor has reached or exceeded a predetermined maximum temperature, TS_(MAX), for a predetermined period of time, Δ_(ts), and ii) the temperature in the combustion chamber as measured by the thermopile has also reached or exceeded a predetermined maximum temperature, TP_(MAX), for the predetermined period of time, Δ_(tp).
 9. The gas fueled water heater of claim 1, wherein the thermistor is supported by the chamber wall.
 10. The gas fueled water heater of claim 9, wherein the sheath is attached to the chamber wall.
 11. The gas fueled water heater of claim 10, wherein the sheath comprises a metal.
 12. The gas fueled water heater of claim 11, wherein the sheath comprises a ceramic.
 13. A gas fueled water heater, comprising: a tank for storage of water for heating; a chamber wall supporting the tank and forming a combustion chamber; a gas burner centrally located within the combustion chamber and positioned below the tank, the gas burner spaced apart from the chamber wall; a thermistor located with the combustion chamber and adjacent to the gas burner without being located within a flame of the burner, the thermistor configured for providing a signal representing temperature within the combustion chamber, wherein the thermistor is not in contact with the chamber wall; and a sheath completely surrounding the thermistor and configured for protecting the thermistor.
 14. The gas fueled water heater of claim 13, further comprising a controller in communication with the thermistor for the receipt of temperature measurements from the thermistor, and a gas valve for controlling the flow of gas to the gas burner; wherein the controller is in communication with the gas valve and is configured to close the flow of gas through the gas valve upon determining that the temperature in the combustion chamber as provided by a signal from the thermistor has reached or exceeded a predetermined maximum temperature, TS_(MAX).
 15. The gas fueled water heater of claim 13, further comprising a controller in communication with the thermistor for the receipt of temperature measurements from the thermistor, and a gas valve for controlling the flow of gas to the gas burner; wherein the controller is in communication with the gas valve and is configured to close the flow of gas through the gas valve upon determining that the temperature in the combustion chamber as determined from a signal provided by the thermistor has reached or exceeded a predetermined maximum temperature, TS_(MAX), for a predetermined period of time, Δ_(ts).
 16. The gas fueled water heater of claim 13, further comprising: a pilot burner for providing a pilot light to ignite the gas burner; and a thermopile positioned adjacent to the pilot burner and configured for detecting the presence of a pilot light at the pilot burner and for providing a secondary measurement of temperature in the combustion chamber.
 17. The gas fueled water heater of claim 16, further comprising a controller in communication with the thermistor for the receipt of a signal representing temperature measurements from the thermistor; and wherein the controller is in communication with the gas valve and is configured to close the flow of gas through the gas valve upon determining that both i) the temperature in the combustion chamber as measured by the thermistor has reached or exceeded a predetermined maximum temperature, TS_(MAX), and ii) the temperature in the combustion chamber as measured by the thermopile has reached or exceeded a predetermined maximum temperature, TP_(MAX).
 18. The gas fueled water heater of claim 16, further comprising: a gas valve for controlling the flow of gas to the gas burner; wherein the controller is in communication with the gas valve and is configured to close the flow of gas through the gas valve upon determining that both i) the temperature in the combustion chamber as measured by the thermistor has reached or exceeded a predetermined maximum temperature, TS_(MAX), for a predetermined period of time, Δ_(ts), and ii) the temperature in the combustion chamber as measured by the thermopile has also reached or exceeded a predetermined maximum temperature, TP_(MAX), for the predetermined period of time, Δ_(tp). 